CFHT introduced the New Observing Program (NOP) in 2001 with the goal
of increasing the quality of the data produced at the telescope and
delivered to the astronomer. The NOP includes low-level improvements
to the camera and telescope interfaces (NEO and TCS IV) which are
mostly hidden from the observers, as well as high-level advances in
how the data are taken, with the introduction of the Queued Service
Observing (QSO). A major component of the NOP is Elixir, an extensive
data assessment, calibration, and pre-processing system.

The Elixir system, illustrated below, provides three types of
services: 1) real-time data quality assessment, 2) end-of-run detailed
calibration analysis, 3) image pre-processing and meta-data
compilation for data distribution. Coupled with the data analysis
pipelines are various databases which store all of the necessary data
products. This document provides an overview of the Elixir system
components.

Real-time Analysis The real-time data quality assessment
provides quick information to the observers, including the image
quality for each image taken, along with tools to make the
observations easier: focus analysis plots and real-time data summary
plots. In addition, the real-time image statistics pipeline adds data
about each image and CCD to a database of image statistics, used by
other Elixir systems to select image subsets for further analysis.
The real-time system for MegaPrime also includes an analysis pipeline
which provides detrended images to the teams involved in the CFHT
Legacy Survey supernova searches.

Master Detrend Creation The end-of-run analysis starts with
the generation of the master detrend frames. The image statistics
database is used to select possible input frames which are combined to
create master bias, dark, and flat-field images, which are then
applied to the original input frames. The Elixir team may then
interactively include or exclude a subset of the original input images
based on these residual images to generate the best possible master
detrend frames, which is then stored in another database. A similar
system generates the master fringe frames.

Detailed Image Analysis The second stage provides the
astrometric calibrations and extracts the stellar photometry. The
data processing pipeline for this stage uses the master detrend frames
from the previous stage to flatten all of the science images from the
camera run. Object detection and instrumental photometry is performed
on the flattened images using Sextractor (Bertin \& Arnouts 1996).
These objects are used to determine the astrometric solution, by
comparison with the USNO 1.0 or other references. The astrometrized
object detections are added to the Elixir photometry database system,
DVO.

Standard Star Analysis The end-of-run analysis also includes
the standard star analysis and the determination of the nightly zero
points. Observations of standard stars are extracted from the
photometry database and used to determine the zero-points for each
standard star image. The zero-point values reflect the changes in the
night-time transparency, if any, as well as any long-term changes in
the telescope or optical transmission. We find that a single airmass
and a single, non-varying set of color terms have so far been
sufficient to define the standard-star photometry. The Elixir system
records the statistics for each standard star frame as well as the
statistics from all frames in a filter for each night. These values
are saved in separate database tables.

Data Distribution The data distribution system uses an Elixir
pipeline to perform the image pre-processing, using the best master
detrend images available. The same processing pipeline also inserts
header keywords giving the astrometric and photometric calibrations
determined in the end-of-run stage. The pipeline also generates
thumbnail jpeg images which are used by the data processing system to
generate a data summary report in a web page interface.